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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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890                                  ALASKAN GLACIER STUDIES
about 15 miles east of Cordova (PL XCHI), terminating a little over 2 miles north of the railway. It has been briefly mentioned and sketched upon maps by Abercrombie 1 in 1884 and 1898, Seton Karr3 in 1886, and Witherspoon3 in 1900 and 1911. Our own observations are based upon two days work in 1910 by the junior author and general views from the railway in 1909 and 1911.
VaRey Portion. The glacier has a well-defined valley portion, rising in snowfields 5000 or 6000 feet above sea level and supplied by at least two main tributaries. Four or five cascading ice tongues reach the glacier, and there are two or three hanging glaciers which no longer supply ice to it. The valley tongue of Sheridan Glacier is about a mile wide and at least 5| miles long. It is clean and little crevassed and has one weak medial moraine near the eastern margin.
Bulb-Shaped Terminus. Beyond the mountain face the glacier expands into a bulb-shaped terminus, sloping in all directions from the mouth of the valley. This bulb, is over 4 miles long and 8 miles wide, terminating about 150 feet above sea level. Most of its surface is without moraine and it was little crevassed in 1910. The terminus, however, bears a narrow band of ablation moraine, broadest near the western edge. Close to the front of Sheridan Glacier bulb is a low, narrow terminal moraine, covered with a thick growth of alder, cottonwood and some conifers.
Seton Karr's drawing and description of the glacier in 1886 * makes it clear that the expansion of the bulb took place more than 25 years ago and that there has been little recession since that time. The presence of thick mature forest up to the very edge of the bulb indicates that the glacier has not been more extensive for a score of years, perhaps for a century. A comparison of photographs shows that there was no significant change between 1908 and 1910, with the exception of a slight thinning by ablation; and there was no visible change from 1910 to 1911. At the very front of the glacier, and east of the middle, is a great rock knob to the summit of which the ice rises, but without passing over it or covering the southern side. This knob gives a convenient basis for deter-mining future oscillations of the front of Sheridan Glacier in the way of moderate advance or of a continuation of the very slight recession which has characterized the recent history of the glacier.
Outwash Plain. Between the glacier and the sea lies an extensive outwash plain. The stream from the eastern edge of Sheridan Glacier, probably also carrying the drainage from Sherman Glacier, is building an extensive alluvial fan which is separated from the main outwash gravel plain by a line of forest-covered hills near Mile 17, several hundred feet high. A number of other knobs and spurs rise like islands through the out-wash gravels. East of fhia alluvial fan, the railway crosses several low ridges, some of till, some of rounded gravels, and a few of rock, and all densely forested. It is clear that these unconsolidated ridges represent remnants of a terminal moraine of an eastward
i Abercrombie, W. R., Report of a Supplementary Expedition into the Copper River Valley, Alaska. Narratives of Explorations in Alaska, Senate Rept. 1023, 56th Congress, 1st Session, Washington, 1900, p. 384; Ibid., War Dept., Adj.-Gen. Office, No. XXV, 1899, map in pocket.
* Seton Karr, H. W., Shores and Alps of Alaska, London, 1887, pp. 169-171.
* Witherspoon, D. C., PI. n in House Doc. 546,56th Congress, 2nd Session, 1901; also in Bull. 374, U.,8. Geol Survey, 1909, PI. I; for detailed map made in 1911, see Brooks, A. H. and others, Railway Routes in Alaska, House Doc. 1S46, Fort 2, 62nd Congress, 3rd Session, Washington, 1918, Plate 5.
ŤOp. ciL, p. 171.